BH4 domain peptides derived from Bcl-2/Bcl-XL as novel tools against acute pancreatitis

Abstract

Biliary acute pancreatitis (AP) is a serious condition, which currently has no specific treatment. Taurolithocholic acid 3-sulfate (TLC-S) is one of the most potent bile acids causing cytosolic Ca2+ overload in pancreatic acinar cells (PACs), which results in premature activation of digestive enzymes and necrosis, hallmarks of AP. The inositol 1,4,5-trisphosphate receptor (IP3R) and the ryanodine receptor (RyR) play major roles in intracellular Ca2+ signaling. Inhibition of these endoplasmic reticulum-located channels suppresses TLC-S-induced Ca2+ release and necrosis, decreasing the severity of AP. Anti-apoptotic B-cell lymphoma (Bcl)-2-family members, such as Bcl-2 and Bcl-XL, have emerged as important modulators of IP3Rs and RyRs. These proteins contain four Bcl-2 homology (BH) domains of which the N-terminal BH4 domain exerts critical roles in regulating intracellular Ca2+ release channels. The BH4 domain of Bcl-2, but not of Bcl-XL, binds to and inhibits IP3Rs, whereas both BH4 domains inhibit RyRs. Although clear cytoprotective effects have been reported for these BH4 domains, it remains unclear whether they are capable of inhibiting pathological Ca2+-overload, associated with AP. Here we demonstrate in PACs that the BH4 domains of Bcl-2 and Bcl-XL inhibit RyR activity in response to the physiological agonist cholecystokinin. In addition, these BH4 domains inhibit pathophysiological TLC-S-induced Ca2+ overload in PACs via RyR inhibition, which in turn protects these cells from TLC-S-induced necrosis. This study shows for the first time the therapeutic potential of BH4 domain function by inhibiting pathological RyR-mediated Ca2+ release and necrosis, events that trigger AP.

Therapeutic implications of novel peptides targeting ER–mitochondria Ca2+-flux systems

“…Acute pancreatitis does not only occur in response to high fat and/or alcohol consumption but also as an adverse event in Lasparaginase treatments of children with acute lymphoblastic leukemia [68,69]. Recently, we showed that the BH4 domain of Bcl-2 and Bcl-XL can be used to suppress pathological bile-acid-induced RyRmediated Ca 2+ release in pancreatic acinar cells, thus preventing necrosis, a hallmark in the development of acute pancreatitis [70]. This nicely illustrates the therapeutic potential that drugs mimicking BH4 domain functions at ER Ca 2+ -release channels can hold.…”

Directly targeting BAX for drug discovery: Therapeutic opportunities and challenges

“…Alanine scanning mutagenesis data has identified I19 and L23 of the Bcl-2 BH4 domain as critical residues for stabilizing its binding to BAX 135 . Furthermore, BH4 domain peptides from Bcl-2/Bcl-X L have been found to inhibit excessive activation of ryanodine receptor (RyR) to block pathological taurolithocholic acid 3-sulfate (TLC-S)-induced) Ca 2+ release, thereby protecting pancreatic acinar cells from TLC-S-induced necrosis 136 . This finding underscores the anti-apoptotic function of the Bcl-2 BH4 domain.…”

The role of Ca2+ signalling in the pathology of exocrine pancreas

“…Another direction, currently quickly developing, is the Bcl-2 dependant regulation of Ca 2+ release. The anti-apoptotic members of B-cell lymphoma (Bcl)−2-proteins, Bcl-2 and Bcl-extra-large (Bcl-XL) have been established as endogenous negative regulators of IP3Rs and RyRs [ 93 , 94 ]. We have demonstrated previously that Bcl-2 is involved in the regulation of calcium extrusion in PACs [95] , an effect that would also be useful in the inhibition of Ca 2+ overload.…”

“…To emulate the action of the BH4 domain of Bcl-2 and Bcl-XL, BH4 domain-derived peptides were employed to demonstrate the effectiveness of the BH4 domain in inhibition of IP 3 Rs in different cell types [ 93 , 98 ]. We have recently shown that both the BH4 domain derived peptides (50µM) of Bcl-2 and Bcl-XL significantly reduced excessive Ca 2+ release from internal stores as well as PACs’ necrosis induced by the bile acid Taurolithocholic acid 3-sulfate (TLC-S), demonstrating a therapeutic potential of this approach [94] .…”